The subject invention relates to a practical process of anionic synthesis of stable macrocyclic diene and vinyl aromatic polymers and copolymers using cyclic organometallic polymerization initiators containing metals of Group IIA and IIB of the Periodic System. More particularly, the invention relates to the formation of coupled/functionalized macrocyclic polymers that may be compounded to produce vulcanizable elastomers exhibiting low hysteresis properties. Such elastomers, when used to form articles, such as tires, shock absorbers, mounts, power belts and the like, will show an increase in rebound, a decrease in rolling resistance and have less heat build-up when mechanical stresses are applied.
Previous attempts at preparing reduced hysteresis compounds have included high temperature mixing of the filler-rubber mixtures in the presence of selectively-reactive promoters to promote compounding material reinforcement, surface oxidation of the compounding materials, and chemical modifications to the terminal end of polymers using 4,4'-bis(dimethylamino)-benzophenone (Michler's ketone), tin coupling agents and the like, and surface grafting thereon. All of these approaches have focused upon increased interaction between the elastomer and the compounding materials.
It has also been recognized that carbon black, employed as a reinforcing filler in rubber compounds, should be well dispersed throughout the rubber in order to improve various physical properties. This dispersion can be achieved, for example, by endcapping polydienes by reacting a metal terminated polydiene with a capping agent, such as a halogenated nitrile, a heterocyclic aromatic nitrogen-containing compound or a trialkyl tin halide. Additionally, it is known in the art that both ends of the polydiene chains can be capped with polar groups by utilizing functionalized anionic initiators, such as lithium amides.
In another approach, lithium amino magnesiate anionic polymerization initiators, stable at high polymerization temperatures, have been employed to produce polymers containing a high level of tertiary amine functionality with functional end groups derived from the initiator. Such polymers can be compounded to produce vulcanizable elastomers exhibiting reduced hysteresis properties. This approach is disclosed in U.S. Pat. No. 5,610,227, the disclosure of which relative to functionalizing of polymers is hereby incorporated by reference.
A need still exists, however, for methods of preparing polymers and vulcanizable elastomers that exhibit reduced hysteresis properties.